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71.
Cd-doped Tl0.9Bi0.1Sr1.8Yb0.2Ca1−xCdxCu1.99Fe0.01O7−δ (x=0–0.4) bulk superconductor samples were prepared by solid-state reaction method, to examine the effect of Cd on ultrasonic velocity and elastic behavior of the samples. The samples were characterized by X-ray diffraction, DC electrical resistivity and temperature dependent ultrasonic velocity measurements. DC electrical resistivity measurement showed all the samples exhibit metallic normal-state behavior with the highest Tc zero observed at around 76.4 K (x=0.3). Ultrasonic velocity measurements at 80 K showed a non-linear increase in both absolute longitudinal and shear velocities as well as elastic moduli with Cd substitution with the largest increase observed for the x=0.3 sample. Temperature dependant longitudinal modulus showed elastic anomaly characterized by a step-like slope change at around 230 K for x=0 & x=0.3 and at around 250 K for x=0.4 with the x=0.3 sample showing the sharpest slope change. A comparison between experimental data and calculated lattice anharmonicity curve based on the model proposed by Lakkad, showed large deviation of the experimental longitudinal modulus curves for (x=0.3) from the calculated anharmonicity curves indicating that the elastic behavior was strongly influenced by the existence of the step-like longitudinal anomaly. On the other hand, our analysis using the Landau free energy model found that the anomalous step-like elastic behavior fitted well with the equation derived from the model for regions below and above the elastic anomaly temperature, TA. The fitting indicated that the anomaly is related to a phase transition that is suggested to involve ordering of oxygen which introduces strain in the system. 相似文献
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Jung-Ryul Lee He-Jin Shin Chen Ciang Chia Dipesh Dhital Dong-Jin Yoon Yong-Hak Huh 《Optics and Lasers in Engineering》2011,49(12):1361-1371
Wind turbine blade failure is the most prominent and common type of damage occurring in operating wind turbine systems. Conventional nondestructive testing systems are not available for in situ wind turbine blades. We propose a portable long distance ultrasonic propagation imaging (LUPI) system that uses a laser beam targeting and scanning system to excite, from a long distance, acoustic emission sensors installed in the blade. An examination of the beam collimation effect using geometric parameters of a commercial 2 MW wind turbine provided Lamb wave amplitude increases of 41.5 and 23.1 dB at a distance of 40 m for symmetrical and asymmetrical modes, respectively, in a 2 mm-thick stainless steel plate. With this improvement in signal-to-noise ratio, a feasibility study of damage detection was conducted with a 5 mm-thick composite leading edge specimen. To develop a reliable damage evaluation system, the excitation/sensing technology and the associated damage visualization algorithm are equally important. Hence, our results provide a new platform based on anomalous wave propagation imaging (AWPI) methods with adjacent wave subtraction, reference wave subtraction, reference image subtraction, and the variable time window amplitude mapping method. The advantages and disadvantages of AWPI algorithms are reported in terms of reference data requirements, signal-to-noise ratios, and damage evaluation accuracy. The compactness and portability of the proposed UPI system are also important for in-field applications at wind farms. 相似文献
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The activation energy is the minimum amount of energy required to initiate a reaction. It is one of the important indexes for appraising a reaction. The chemical reaction rate is closely related to the value of activation energy, and reducing activation energy is propitious to promoting a chemical reaction. In the present paper, the relationship between the activation energy in Si-KOH reaction system and the ultrasound frequency and power has been discussed for the first time. The range of ultrasound frequency and power is 40-100kHz (interval by 20kHz) and 10-50W (interval by 10W), respectively. The experimental clata indicate that the activation energy decreases with the increasing ultrasound power. Comparing with the activation energy without ultrasound irradiation, the results in our paper indicate that ultrasound irradiation could reduce the activation energy in Si-KOH reaction system and increase the reaction rate. 相似文献
78.
Shadpour Mallakpour Fariba Derakhshan 《International Journal of Polymer Analysis and Characterization》2014,19(8):750-764
In this study, the goal was the preparation, characterization, and surface morphology of poly(amide-imide)/TiO2-citric acid nanocomposites (PAI/TiO2-CA NCs). Owing to the high surface energy and tendency for agglomeration, the surface of TiO2 nanoparticles was modified with citric acid. Then poly(amide-imide) was synthesized by direct polycondensation reaction of N,N′-(pyromellitoyl)-bis-L-leucine diacid with 4,4′-diaminodiphenylmethane by triphenyl phosphite and tetra-n-butylammonium bromide as a green medium. The attained polymer and modified TiO2 nanoparticles were used to prepare PAI/TiO2-CA NCs through ultrasonic irradiation. The resulting PAI/TiO2-CA NC was characterized with FT-IR spectroscopy, X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, and thermogravimetric analysis. 相似文献
79.
高效液相色谱-电感耦合等离子质谱法分析海洋沉积物中有机锡的形态 总被引:4,自引:0,他引:4
建立了高效液相色谱-电感耦合等离子质谱(HPLC-ICP-MS)测定海洋沉积物中二丁基锡(DBT)、三丁基锡(TBT)、二苯基锡(DPhT)及三苯基锡(TPhT)的形态分析方法。通过改变流动相组分比例,使4种有机锡达到基线分离。比较不同提取方法对标准参考物质PACA-2中有机锡的提取效率。以V(乙腈)∶V(H2O)∶V(乙酸)=55∶33∶12(含5%三乙胺,pH 3.0)为提取剂时,超声提取效率最高(>91.5%),其加标回收率均大于96%。本方法对DBT,TBT,DPhT和TPhT的检出限分别达到0.7,0.75,0.45和0.4μg/kg。对浓度范围为0.5~100μg/kg有机锡混合标准溶液进行测定,4种有机锡回归系数均大于0.998。利用本方法对几种海洋沉积物样品和海产品中的有机锡进行测定,在部分沉积物样品中检测到了DBT和TBT,部分海产品中测到了少量TBT和TPhT。 相似文献
80.
采用超声搅拌化学浴法(UCBD)在SnO2:F透明导电玻璃衬底上制备了CdS薄膜.研究了退火和CdCl2处理对UCBD-CdS薄膜的表面形貌、晶体结构和直接带隙的影响,比较了沉积时间对UCBD-CdS薄膜中CdS聚集体颗粒大小和堆积致密性的影响.结果表明,CdCl2处理可使CdS聚集体中的小颗粒重新熔合在一起,但CdS聚集体的大小并没有改变.在UCBD-CdS薄膜的沉积过程中,CdS薄膜的横向和纵向生长速率之比会随着沉积时间的不同而改变,且沉积时间是获得大颗粒的CdS聚集体和致密的UCBD-CdS薄膜的重要影响因素.当沉积时间为40min时,获得的UCBD-CdS薄膜较致密,CdS聚集体的大小为180nm,膜厚为80.8nm,适合作为薄膜太阳电池的窗口层. 相似文献